1. Field of the Invention
This invention relates to an improved fluid flow sensing switch device and method of making the same as well as to a fuel control system utilizing such device for controlling the operation of electrical ignition means for a burner means of the fuel control system.
2. Prior Art Statement
It is known to provide a fluid flow sensing switch device having a housing means provided with a fluid flow passage therethrough defined by an inlet and an outlet separated by a valve seat controlled by a movable valve member that is operated by the pressure differential between the inlet and the outlet, the device having an electrical switch construction operatively associated with the valve member and having contact means thereof actuated by the pressure differential.
For example, see the following four United States Patents:
(1) U.S. Pat. No. 3,898,403--Grayson et al
(2) U.S. Pat. No. 1,938,327--Green
(3) U.S. Pat. No. 3,551,620--Hoover
(4) U.S. Pat. No. 3,164,414--Stelzer.
The fluid flow sensing switch device of item (1) above, appears to be utilized in a fuel control system for a burner to operate the electrical ignition means of the burner upon a pressure drop being created between the inlet and the outlet of the fluid flow sensing switch device by the operator opening the "on-off" valve that leads to the burner, the fluid flow sensing switch device having a magnetically operated electrical switch mounted external to the main housing thereof and being controlled by the pressure differential between the inlet and the outlet in such a manner that the switch construction closes its contacts to operate the electrical ignition means before the pressure differential opens the valve member away from the valve seat to direct full fuel flow to the burner.
However, see column 5, lines 33-39, of item (1) above which states:
"Note will be taken that the magnetically operated switch may be replaced with a mercury switch or any other utilization device inside or outside the fluid housing. For example, if the mercury switch is inside the housing, pigtail electrical leads may extend completely through the housing in sealed relation thereto."
It appears that the fluid flow device of item (2) above has one of the contacts of the electrical switch thereof carried by a flexible diaphragm that controls the position of a valve member relative to the valve seat intermediate the inlet and outlet thereof, the electrical contacts of the switch construction being remote from the inlet and outlet of the device.
Similarly, the fluid flow device of item (3) appears to have a magnetically operated reed switch mounted remotely from the inlet and outlet of the device, the magnet being carried by flexible diaphragm that controls the position of the valve member relative to the valve seat that is disposed intermediate the inlet and outlet of the device.
It appears that the fluid flow device of item (4) above has a diaphragm that carries an electrical contact that will be moved with the diaphragm into electrical contact with a fixed contact when the pressure differential acting across the diaphragm increases a certain amount. Thereafter, a spring biased valve member carried by the diaphragm will open to permit fluid flow from an inlet through the diaphragm over the closed contacts and out an outlet, the fluid flow device of item (4) being for controlling the flow of compressed air therethrough for operating a trailer brake system or the like.
It is also known to provide a pneumatically operated relay having electrical contacts disposed in the chambers thereof to be engaged by a conductive diaphragm fluidically operated in the relay construction.
For example, see the following United States patent:
(5) U.S. Pat. No. 4,000,386--Brouwer
It appears that the relay of item (5) above has a conductive diaphragm that is adapted to make contact with one or more electrical contacts disposed in fluid chambers defined by the diaphragm for completing electrical logic circuits.